FCTs have no effect on Trainz Store downloads such as DLC or TRS19 purchases. They are always sent at the fastest possible speed that your connection will allow.
I know nothing about your particular link to the Internet but is it possible that you have exceeded your monthly download limit (if you have one) and your ISP is putting you in the slow lane until next month? There are other possibilities that others could explain better than I. Do you use a download manager for your downloads? These will (usually) restart a failed download at the point where the failure occured so you do not have to start all over again?
